A hobbies/sports pack would be wonderful if done right. And that, "done right" is something they rarely do.
They'd need to put in actual work and new features and animations for it to be enjoyable and you know, read the 101 gaming design book. This isn't asking for a trip to Mars, it wouldn't be difficult to make a hobbies pack that is enjoyable it's just that they don't put in work for this game anymore and TS4 even with all the BG design flaws could be more enjoyable.
They could put in special skills in the game that take a lifetime almost to max. For example, start as a white belt as a kid and only when you get to YA you'd get to be a black belt in sim-karate. Make it so that kids-YA can enter competitions with other sims, earn medals and cash rewards for winning big competitions. They could do the same for other key activities/sports. Add interests and hobbies so that sims have more specific things they like and don't, so that making friends is easier or harder, deepening the socializing system. Add a lifetime aspiration meter with a new whim system, etc.
It's too bad everything and anything is too hard or too expensive these days, somehow in 2004 they weren't.